Screening apparatuses are known in the art. Common uses for screening apparatuses include separating grades of coal. Coal is separated at numerous points including de-slime coal, raw coal, clean coal, and refuse coal. Once coal is mined, the coal is subjected to crushing operations in the presence of water. The crushed coal is fed to a separating apparatus to remove fines and to separate the coal particles according to size. Apparatuses used to separate coal by size typically have dangerous moving parts which vibrate the coal over the screening apparatuses.
Separating devices using screens which use gravity partially, or entirely, in their functioning are known in the art. U.S. Pat. No. 7,571,816B2 teaches an adjustable coal screening apparatus that has an adjustable angle of the device to vary the speed of flow of the coal particles downwardly over the screening assembly; the coal screening apparatus is designed to slow down the flow of coal to allow more coal to go through the screen without damaging the screen. This device is used to dewater the coal particles and to separate partial flows to separate paths by means of an improved screen arrangement, and requires a subsequent separating, or screening apparatus, to separate coal by size in addition to dewatering the coal slurry.
U.S. Pat. No. 4,322,288A teaches an apparatus for sizing particulate material such as grain, seeds and the like which includes a movable diverter disposed between upper and lower sets of screens; the material to be sized is advanced using gravity. This device uses the diverter to direct material through a first sizing screen directed toward and discharge pan and material which has not passed through the first sizing screen is directed to a second sizing screen, so that the material may be separated according to size.
Other devices rely almost exclusively on vibration or sharp movements. For example, U.S. Pat. No. 5,501,343A shows a soil feeding apparatus with interrupter, which departs a sudden inertial shock, and is used to separate soil. U.S. Pat. No. 4,498,981A teaches a vibrating anti-blending cleaning and grading machine to separate grain, seed and like particulate cleaning and grading machine. U.S. Pat. No. 6,575,304B2 teaches a vibrating screen apparatus which minimizes the moving parts therein. U.S. Pat. No. 6,736,269B2 shows a device for collecting and recycling articles directed to feeding channels, and is used to separate tablets, capsules, pills, etc. U.S. Pat. No. 7,168,569B2 teaches a vibratory screening machine for earth drilling installation associated with, for example, oil drilling. U.S. Pat. No. 7,331,469B2 discloses a vibratory separator. U.S. Pat. No. 7,380,672B2 teaches a flow diverter and exhaust blower for vibrating screen separator assembly.
U.S. Pat. No. 1,719,513A teaches a coal screen which vibrates and passes coal from a higher level screen to a lower level screen that serves to permit a change of direction of the stream of coal. U.S. Pat. No. 3,204,764A teaches a coal cleaning apparatus which uses screens and a vibratory mechanism to facilitate cleaning coal. U.S. Pat. No. 7,665,614B2 teaches a screening arrangement in a vibrating screen for screening material. US Patent Application No. 2009026113A1 teaches an extra-large vibrating screen with duplex statically indeterminate mesh bream. The international patent application under the PCT Publication No. WO2009051576A1 teaches a screen mesh and method for resonance excitation thereof.
Great Briton (GB) Patent No. 286,544 teaches improvements in and relating to screens or riddles for use in the classification coal, ores, minerals and the like, in which utilizes graduated size screens subject to shaking or jogging. GB Patent No. 297,330 discloses a clay removing apparatus which utilizes screens and an oscillating motion. GB Patent No. 360,403 teaches improvements relating to jigging mechanisms that is used to jiggle a cleaning table for coal and the like. GB Patent No. 498,523 teaches improvements in and related to the separation of solids from liquids that uses downwardly sloping screens and a vibratory mechanism. GB Patent No. 190913840 teaches improved screen conveyors which were used to screen and size coal, and includes a vibrating device to shake the device. Similarly, GB Patent No. 191122386 shows improvements in coal and like screens and conveyors which also uses jiggling/vibrating screening machinery.
The prior art screening devices have apparatuses designed to shake them. Such shaking apparatuses are inherently dangerous. The possibility of a worker getting caught by the shaking device is a constant concern. Another concern is the possibility of a worker in the process of cleaning a conventional screening device is the danger posed by falling into the screens and becoming caught in the flow of coal or other material to be separated.